Field of the Invention
The present invention relates to a technique for improving image quality of when still display (freeze display) is performed on a display screen.
Description of the Related Art
In a recent video processing apparatus, a data size handled in a system has a tendency to increase according to increase in resolution and precision of image processing. For example, regarding the resolution, there are quad full high definition (QFHD, 3840 pixels*2160 lines) and super high vision (7680 pixels*4320 lines). These resolutions require a data processing amount 4 or 16 times greater than that of a video of an existing high definition (HD, 1920 pixels*1080 lines).
Further, regarding increase in precision of image processing, processing for improving image quality is performed by using a plurality of frames as reference images. For example, according to the interlace-to-progressive conversion (IP conversion) and the double speed processing for generating an intermediate frame, a high precision interpolation image is generated by generating motion vectors with reference to a plurality of intermediate frames stored in a memory. In a super resolution technology, high resolution processing with high sharpness is realized by referring to a plurality of image frames and performing matching processing. In order to realize such advanced image processing, numerous intermediate frames are required to be stored in a memory and read out therefrom, so that a data processing amount will increase.
If such a system which can implement both of the above-described processes for increasing resolution and improving image quality is constructed, there is an issue that required memory capacity and memory bandwidth are increased in a video processing apparatus. Thus, methods using a compression and decompression technique are discussed in order to reduce data amounts which are written into and read out from a frame memory.
Japanese Patent Application Laid-Open No. 2010-171609 discusses a video processing system which compresses input video data to write it into a frame memory and performs video processing by decompressing the video data read out from the frame memory.
Japanese Patent Application Laid-Open No. 2010-171609 also discusses a fact that, when a video is displayed on a still screen or a video is displayed on a high definition television, a setting for increasing a video compression ratio is performed, whereas if the apparatus needs to suppress power consumption to drive a battery, a setting for decreasing the video compression ratio is performed.
Japanese Patent Application Laid-Open No. 2000-308016 discusses a fact that, when a pause instruction (still image mode selection) is issued during display of a Moving Picture Experts Group (MPEG) compressed video, an intra-coded picture is displayed from among the I picture, a predictive coded picture (P picture), and a bidirectionally predictive coded picture (B picture)
However, there is a possibility that quality of a video frame to be displayed during temporary stop in response to a pause instruction to temporarily stop video reproduction becomes low.
For example, if a pause instruction for temporary stop is input when a compression ratio of a video frame in a frame memory is temporarily high because of occurrence of a scene change or the like, there is a risk that a video frame having poor quality in the frame memory is displayed during the temporary stop.